Conductive filter element and filter device having a filter element

ABSTRACT

The invention relates to a filter element ( 20 ), comprising individual components ( 2, 4, 8 ), such as a filter medium ( 8 ) as one component and further filter element components ( 2, 4 ), of which at least one component ( 4 ) is made of a material that is at least partially transparent to laser light and at least one further component ( 2 ), in the manner of a barrier layer, is made of a material that is at least partially opaque to laser light in order to perform a transmission welding method by means of laser light for the purpose of connecting associable filter elements to each other, wherein said method is characterized in that at least some of the components of the filter element that are exposed to the laser light during the transmission welding method are at least partially electrically conductive.

The invention relates to a filter element and a filter device having such a filter element. The filter element comprises individual components, such as a filter medium as the one component and additional filter element components, of which at least one component is made of a material which is at least partially transmissive to laser light, and at least one additional component, designed in the manner of a barrier layer, is made of a material that is at least partially non-transmissive to laser light in order to carry out a transmission welding process by means of laser light for the purpose of bonding associable filter element components to each other.

Filter elements are used in many fields of engineering for filtration of a wide variety of dissimilar fluids. Some examples of such fluids include hydraulic fluids, lubricants, and fuels. When the fluid flows through a filter medium of the filter element, an electric voltage can be built up; and in worst case scenarios this electric voltage can assume a value that leads to at least a partial destruction of the filter medium or even the filter element. This situation can arise, especially if the charges, generated during the formation of the voltage, cannot be dissipated in a suitable manner from the filter element. In order to overcome the problem of the generation of the aforementioned voltages, it is known to provide the filter medium with a certain conductivity by, for example, introducing conductive wires and to induce a dissipation of the charges accumulating at the filter medium by means of suitable—usually metallic—additional filter element components. Another requirement of such filter elements is that it should be possible to manufacture them at a low cost and in large quantities. In order to satisfy the latter requirement, it has proven to be expedient to bond together—for example, by adhesively cementing—the individual components of a filter element. However, the prior art solutions are often cost-intensive and present a significant recycling problem due to the use of a plurality of dissimilar materials.

DE 10 2007 013 178 A1 discloses a method for producing a filter element conforming to the type described in the introductory part and comprising the steps: providing a filter medium that surrounds an inner filter cavity and contains a heat sealable material; providing at least one end cap, which forms a covering of the filter cavity on at least one end, the end cap being made of a laser transmissive thermoplastic material; forming a laser non-transmissive barrier layer between the end cap and the adjacent end of the filter medium; welding the end cap and the filter medium by irradiating a laser transmissive material, which is adjacent to the barrier layer, with laser energy in such a way that by heating the region adjacent to the barrier layer, a welding volume is made available as a joining element for the welded joint produced by laser transmission welding. To form the barrier layer, a welding film that is non-transmissive to laser light can be inserted between the end cap and the adjacent end of the filter medium.

Since the filter element components are bonded together by means of laser light by a transmission welding process, an economical production is ensured. It is known from the prior art to join the filter elements to each other with an epoxy resin adhesive. However, in contrast to the laser transmission welding method, this method has many drawbacks. For example, this method has a high space requirement for the reaction accumulators, storage areas for the adhesively cemented filter elements, and the adhesive. In addition, this method is very time-consuming, so that the production costs are correspondingly high. The advantages of laser transmission welding lie in the low thermal and mechanical stress on the associable filter element components that are to be bonded together and in the flexibility of laser transmission welding as well as the possibility of its automation and integration into existing production sequences. With regard to the financial aspect, the expenses incurred for the adhesive and the reaction accumulators are eliminated; in addition, there are no cleaning costs or maintenance costs, as is the case with cementing. Furthermore, the laser transmission welding process has shorter cycle times.

Based on the prior art, the object of the present invention is to provide a filter element and a filter device having such a filter element, so that not only an economical production of the filter element is guaranteed, but that it is also ensured that the filter element will operate reliably. In particular, the buildup of voltages at the components of the filter element that can lead to the destruction of said filter element will be eliminated. This object is achieved by a filter element that has the features disclosed in the independent claim 1 in its entirety and by a filter device having the features specified in claim 12 in its entirety.

Since at least some of the components of the filter element that are exposed to the laser light during the transmission welding operation are at least partially electrically conductive, it is possible to carry out a reliable dissipation of the charges generated at the filter medium.

In an embodiment of the filter element according to the invention, the barrier layer generates heat due to the absorption of laser light and serves at least partially as a bond relative to adjacent adjoining additional filter element components. The result is that the barrier layer melts either superficially or completely; and due to the heat transfer to the adjacent adjoining additional filter element components, these, too, are melted at least in certain regions and can form a bond with each other or with the barrier layer by means of welding.

In an embodiment of the filter element according to the invention, the barrier layer is at least partially electrically conductive. Since the barrier layer is designed to be at least partially electrically conductive, charges can be dissipated from the filter element components that are bonded together by means of the barrier layer.

In an embodiment of the filter element according to the invention, the barrier layer, designed in the manner of a film, is inserted between the filter element components that are to be bonded together by means of laser light by the transmission welding method. In particular, if films having a thickness of less than 0.2 mm and preferably of about 0.05 mm are used for the barrier layer, then such a film will readily adapt to the contours of the filter element components between which said film is inserted and which are to be bonded together.

In an embodiment of the filter element according to the invention, the barrier layer, designed in the manner of a coating, is disposed at least in sections on one of the components of the filter element that are to be bonded together. Such a coating can be produced, for example, by spraying on. In this embodiment, there is no need to insert a barrier layer as a separate part, so that the result is a simplified production of the filter element and a cost reduction.

In an embodiment of the filter element according to the invention, the filter medium is at least partially electrically conductive in order to dissipate charges. As a result, charges, which are generated at the filter medium when a fluid flows through the filter medium, can be passed to adjacent and also at least partially electrically conductive filter element components, so that the generation of voltages, which could lead to a destruction of the filter medium, is effectively avoided. To this end, on the one hand, a conventional filter medium can be interpenetrated by conductive wires, fibers, or even woven fabrics, but, on the other hand, the material of the filter medium itself can be designed so as to be at least partially electrically conductive due to suitable additives that are introduced as early as during the manufacture of said filter medium.

In an embodiment of the filter element according to the invention, at least one of the filter element components is made at least in certain regions of an additive in the form of a synthetic plastic material exhibiting carbon nanotubes and/or carbon fibers and/or steel fibers in order to produce the at least partial electrical conductivity. Such additives have the advantage that they can be readily combined with plastics that are used for manufacturing a filter element or more specifically a filter device. Starting materials that lend themselves well to the addition of such additives include, for example, polystyrene (PS), polyamide (PA), polybutylene terephthalate (PBT), styrene acrylonitrile (SAN), polyether sulfone (PES), acrylonitrile butadiene styrene (ABS), a combination of PC and ABS, a combination of PMMA and ABS, or copolymeric polyacetal (POM). Other additives that have also proven to be successful include carbon fibers.

In an embodiment of the filter element according to the invention, the synthetic plastic material that forms at least one filter element component, which is at least partially electrically conductive, is at least partially transmissive to laser light.

In an embodiment of the filter element according to the invention, a filter element component forms in the manner of an end cap a covering of the filter element on at least one end and, being made of a material that is at least partially transmissive to laser light, is exposed to the laser light during the transmission welding process. The end cap forms, on the one hand, a covering of the filter element on at least one end of the filter element, but also an enclosure for the filter medium on its face side.

In an embodiment of the filter element according to the invention, the end cap is at least partially electrically conductive. As a covering of the filter element, the end cap can be made as one part or as multiple parts—in particular, as one, two, or three parts, with at least one of the parts of the end cap in this embodiment being designed so as to be at least partially electrically conductive so that the charges dissipated from the filter medium can be passed as far as to the outer covering of the filter element. In addition, it can also be provided that at least parts of such an end cap exhibit connecting mechanisms that serve to feed in fluids that are to be cleaned or to remove fluids that have been cleaned. In a preferred embodiment, such connecting mechanisms also have at least one receiving space for a sealant. In particular, such a receiving space can be provided in the form of a recess for an O-ring.

In an embodiment of the filter element according to the invention, at least one of the filter element components is made at least in certain regions of a synthetic plastic material, which has an additive in the form of glass fibers, for the purpose of forming the material that is at least partially non-transmissive to laser light. Just a small amount of glass fibers admixed to the synthetic plastic material causes a decrease in the transmission of laser light through such a material and an increase in the absorption of the laser light, so that when the synthetic plastic material is prepared in such a way, the energy of the laser light is converted preferably into heat.

Lasers that lend themselves well to the transmission welding process with laser light include, for example, solid state lasers such as Nd:YAG lasers with a wavelength of 1,064 nm and high power diode lasers with wavelengths in the range of 800 to 1,000 nm.

In an embodiment of the filter device according to the invention, this filter device comprises an inventive filter element and at least one element receptacle, which is at least partially electrically conductive. Said element receptacle can be connected in a fluid-tight manner to at least one filter element component of the filter element and can be connected in an electrically conductive manner to at least one filter component of the filter element. Due to the electrically conductive connection between the element receptacle of the filter device and the filter element, the charges to be dissipated from the filter element can be dissipated by way of the element receptacle and, thus, from the filter device.

The invention is explained in detail below by means of exemplary embodiments that are shown in the drawings. Referring to the drawings:

FIG. 1 is a highly simplified schematic drawing to explain the transmission welding process by means of laser light;

FIG. 2 is an additional highly simplified schematic drawing to explain the method by which the transmission welding process by means of laser light is carried out;

FIG. 3 is a longitudinal cut of an exemplary embodiment of a filter element according to the invention;

FIG. 4 is a partially cut view of an additional exemplary embodiment of a filter element according to the invention;

FIG. 5 is a partially cut view of an additional exemplary embodiment of a filter element according to the invention;

FIG. 6 is a partially cut view of an additional exemplary embodiment of a filter element according to the invention;

FIG. 7 is a partially cut view of an additional exemplary embodiment of a filter element according to the invention;

FIG. 8 is a partially cut view of an additional exemplary embodiment of a filter element according to the invention;

FIG. 9 shows a first embodiment of an element receptacle of a filter device according to the invention;

FIG. 10 shows a second embodiment of an element receptacle of a filter device according to the invention.

FIG. 1 shows that in the course of the transmission welding process by means of laser light, the laser light 12 of a laser light source 10 penetrates a component 4 that is at least partially transmissive to laser light, before the laser light 12 impinges on a component 2 that is at least partially non-transmissive to laser light. Owing to the absorption of the laser light 12 at the surface of the component 2, heat is generated at the surface of the component so that the surface in the region under discussion begins to melt, with the thermal energy also being passed, according to the drawing in FIG. 1, to the underside of the component 4; and a desired welded joint of the two components is produced by means of a predefined joining pressure F when the melt of the component 2 and the component 4 solidifies.

The component 2 that is at least partially non-transmissive to laser light can be, for example, a plate, a disk, or a film that melts either superficially or completely during the welding process. In the drawing from FIG. 1, the component 2 is designed in the form of a plate, whereas in the drawing from FIG. 2, the component 2, which is designed in the form of a film, is completely melted during the transmission welding operation in order to join together two components 6 and 4. In so far as the components 2, 4 and 6 are designed so as to be at least partially electrically conductive, an electrical charge can be dissipated from the component 4 to the component 2 and/or to the component 6 and/or vice versa.

A laser light-transmissive and simultaneously electrically conductive synthetic plastic material can be made, for example, in that the additives in the form of a specified quantity of carbon nanotubes (CNTs) and/or carbon fibers in the base material of the synthetic plastic material produce a sufficiently electrical conductivity and that the material is transparent to the laser in a specific laser wavelength range.

FIG. 3 is a longitudinal view of an exemplary embodiment of an inventive filter element 20, which is designed so as to be in essence rotationally symmetrical to a central axis 22 and which comprises individual components, such as a filter medium 8 as the one component and additional filter element components 2, 4, 14, 16, and 18. In order to carry out a transmission welding operation with laser light 12 for the purpose of bonding associable filter element components to each other, at least one component 4 is made of a material that is at least partially transmissive to laser light 12 and at least an additional component 2, which is designed in the manner of a barrier layer and is made of a material that is at least partially non-transmissive to laser light 12. In this case, some of the components of the filter element that are exposed to the laser light 12 during the transmission welding process are at least partially electrically conductive. For example, in the embodiment depicted in FIG. 3, the component 4 of the filter element 20 is designed so as to be at least partially electrically conductive. The barrier layer 2 generates heat due to the absorption of laser light and, as a result, serves at least partially as a bond relative to adjacent adjoining additional filter element components, such as the component 4, the filter medium 8, and a support tube 14. The lower end (when viewed in the direction of FIG. 3) of the filter element 20 has an additional component 16, which is non-transmissive to laser light; and this additional component is disposed in the form of an additional barrier 16 between the support tube 14, the filter medium 8, and a lower covering 18. As a result, associated filter element components can also be bonded together in this region.

In an embodiment of the filter element 20 according to the invention, the barrier layer 2 and/or 16 is at least partially electrically conductive, so that this bather layer lends itself well to the transport of charges.

FIGS. 4 and 5 show in each case a partially cut view of additional exemplary embodiments of the conductive filter element 20 according to the invention. This filter element is structurally designed in such a way that an electrical conductivity is provided and that joints can be made by the transmission welding method with laser light. In the embodiments depicted herein, synthetic plastic materials are used for the components that do not have to be simultaneously conductive and transparent to laser light.

According to FIG. 4, an electrically conductive absorbing barrier layer 2 is laid as an additional piece between a laser-transparent end cap, the filter medium 8, and the support tube 14. The end cap 4 is constructed as two parts and has an inner ring 24, which is made of an electrically conductive synthetic plastic material and which can dissipate the electrical charge to a conducting connecting piece 40 (see FIG. 10) of an element receptacle 42 (see FIG. 10). The inner ring 24, the bather layer 2, the support tube 14, and the filter medium 8 are made of an electrically conductive synthetic plastic material. In the interest of cost savings, the lower end cap 26 (when seen in the direction of FIG. 4) can be made of a non-electrically conductive synthetic plastic material, but must be transparent to the laser. In this case, the barrier layer 2 is designed in the manner of a film.

According to the exemplary embodiment from FIG. 5, a three part, preferably injection-molded, O-ring cap is used for the laser light-transmissive component 4. The O-ring cap is constructed with a barrier layer 2 that is sprayed on in the 2-component injection molding process or is inserted as a separate part. The inner ring 24 forms the third part of the O-ring cap. As a result of inserting the inner ring 24 into the O-ring cap, a receiving space 28 is produced for an O-ring. The charge generated at the filter medium 8 is dissipated from the filter medium 8 to the support tube 14 by way of the inner ring 24 on the conducting element connecting piece 40 of the element receptacle 42 (see FIG. 10). Therefore, the components 2, 24, 14, and 8 are made of an electrically conductive synthetic plastic material. The upper component 4 (when viewed in the direction of FIG. 5) of the O-ring cap is made of a laser-transparent synthetic plastic material, so that the laser light 12 can pass to the component 2 of the filter element that is non-transmissive to laser light.

In the exemplary embodiment according to FIG. 6, the inner ring 24 is inserted into the component 4 of the O-ring cap that is transmissive to laser light. The component 2 that is non-transmissive to laser light is attached here to the inner ring 24. During the welding process, the laser penetrates through the component 4 that is transmissive to laser light and melts the barrier layer as the component that is non-transmissive to laser light as a part of the inner ring 24. The resulting thermal energy melts the surface of the laser light-transmissive component 4 in the form of the O-ring cap, the support tube 14, and the filter medium 8. During the solidification of the melt bath, a welded joint is formed between the components. In this configuration of the components, the O-ring cap is designed so as to be laser-transparent, whereas the inner ring 24 is designed to be laser-absorbing. Here the electrical charge is passed from the filter medium 8 over the support tube 14 to the inner ring 24, so that these components are made of an electrically conductive synthetic plastic material. The lower end cap 26 has to be designed so as to be laser-transparent, but not necessarily electrically conductive.

In the additional embodiment from FIG. 7, the inner ring 24 is eliminated, because in this case the support tube 14 is inserted into the component 4 that is transmissive to laser light, so that the receiving space 28 is formed for an O-ring. A component that is non-transmissive to laser light is sprayed in the form of a barrier layer onto the support tube 14. The filter medium 8 and the support tube 14 are made of an electrically conductive material. The electrical charge is dissipated from the support tube 14 to the conducting connecting piece 40 of the element receptacle 42 (see FIG. 9, FIG. 10). The O-ring cap, as the component 4 that is transmissive to laser light, and the lower end cap 26, which is disposed at the opposite face-side end of the filter medium 8, are made of a material that is transmissive to laser light. Since the barrier layer is sprayed onto the support tube 14 by injection molding, there is no need to additionally insert a barrier layer as a separate part, as a result of which the design of the filter element 20 according to the drawing in FIG. 7 has proved to be especially economical.

Even in the embodiment according to FIG. 8, the barrier layer is sprayed, as in FIG. 7, onto the support tube 14, so that here, too, there is no need to insert a separate part as the bather layer that is non-transmissive to laser light. The laser beam penetrates the lower end cap 26, which is transmissive to laser light, and melts the barrier layer. Then this barrier layer bonds the lower end cap 26 to the support tube 14 and the filter medium 8. The electrical charge is passed from the filter medium 8 to the support tube 14. The filter medium 8 and the support tube 14 are made of an electrically conductive synthetic plastic material.

The variants that are depicted in the various exemplary embodiments and that are intended for connecting the O-ring cap as the component 4 that is transmissive to laser light and/or for connecting the lower end cap 26 can also be combined. For this purpose, the variants can also be applied to a filter element 20 with an external support tube (not illustrated). Optionally, the support tube in the variants can also be constructed as two parts in order to ensure the installation of the filter medium 8. To this end, it is especially expedient to design the support tube as two parts in the axial direction. From the viewpoint of cost-effectiveness, a combination of the embodiment from FIG. 7 with the embodiment from FIG. 8 with a barrier layer that is sprayed directly onto the support tube is especially interesting.

FIGS. 9 and 10 show the element receptacles 42 for the filter devices 44 according to the invention, in each case, the element receptacle having a conducting connecting piece 40 that can be connected in a conducting manner to a component of the filter element 20 according to the invention.

In the embodiment according to FIG. 9, the filter medium 8 of the filter element 20 is disposed in a support tube 14; and the O-ring cap 4 has a receiving space 28 into which an O-ring 30 is inserted on the outer circumferential side in the direction of the conducting connecting piece 40 of the element receptacle 42. As a result, the O-ring cap 4, designed in the form of a hollow connecting piece in the region of the O-ring, is brought into sealing contact with a corresponding recess of the conducting connecting piece 40; and at the same time a charge transport from the O-ring cap 4 to the conducting connecting piece 40 of the element receptacle 42 can take place.

In the embodiment according to FIG. 10, the filter medium 8 is mounted on a support tube 14 that lies coaxially on the inside; and the support tube 14 has in turn on its end, adjacent to the connecting piece 40, a receiving space 28 for an O-ring 30. In contrast to the exemplary embodiment according to FIG. 9, the connecting piece 40 of the element receptacle 42 is not attached here externally to the O-ring cap 4, but rather penetrates the O-ring cap 4 in order to rest against the inner wall of the support tube 14 in sealing contact with the O-ring 30. 

1. A filter element (20) comprising individual components (2, 4, 8), such as a filter medium (8) as the one component and additional filter element components (2, 4), of which at least one component (4) is made of a material which is at least partially transmissive to laser light, and at least one additional component (2), designed in the manner of a barrier layer, is made of a material that is at least partially non-transmissive to laser light in order to carry out a transmission welding process by means of laser light (12) for the purpose of bonding associable filter element components to each other, characterized in that at least some of the components of the filter element that are exposed to the laser light during the transmission welding operation are at least partially electrically conductive.
 2. The filter element (20) according to claim 1, characterized in that the barrier layer generates heat due to the absorption of laser light and serves at least partially as a bond relative to adjacent adjoining additional filter element components (4, 8).
 3. The filter element (20) according to claim 1, characterized in that the barrier layer is at least partially electrically conductive.
 4. The filter element (20) according to claim 1, characterized in that the barrier layer, designed in the manner of a film, is inserted between the filter element components (4, 8) that are to be bonded together by means of laser light (12) by the transmission welding method.
 5. The filter element (20) according to one of the claim 1, characterized in that the barrier layer, designed in the manner of a coating, is disposed at least in sections on one of the components (4, 14, 18, 24) of the filter element (20) that are to be bonded together.
 6. The filter element (20) according to claim 1, characterized in that the filter medium (8) is at least partially electrically conductive in order to dissipate charges.
 7. The filter element (20) according to one claim 1, characterized in that at least one of the filter element components (14) is made at least in certain regions of an additive in the form of a synthetic plastic material exhibiting carbon nanotubes and/or carbon fibers and/or steel fibers in order to produce the at least partial electrical conductivity.
 8. The filter element (20) according to claim 7, characterized in that the synthetic plastic material that forms at least one filter element component (14), which is at least partially electrically conductive, is at least partially transmissive to laser light.
 9. The filter element (20) according to claim 1, characterized in that a filter element component (4) forms in the manner of an end cap a covering of the filter element (20) on at least one end and, being made of a material that is at least partially transmissive to laser light, is exposed to the laser light (12) during the transmission welding process.
 10. The filter element (20) according to claim 9, characterized in that the end cap is at least partially electrically conductive.
 11. The filter element (20) according to claim 1, characterized in that at least one of the filter element components (2) is made at least in certain regions of a synthetic plastic material, which has an additive in the form of glass fibers, for the purpose of forming the material that is at least partially non-transmissive to laser light.
 12. A filter device (44) comprising a filter element (20), according to claim 1, and at least one element receptacle (42), which is at least partially electrically conductive; and said element receptacle can be connected in a fluid-tight manner to at least one filter element component of the filter element (20) and can be connected in an electrically conductive manner to at least one filter component of the filter element (20). 